In a medium bowl combine yoghurt, garlic, paprika, salt and pepper and mix well. Add beef and stir to coat. Cover with cling film and marinate for at least 2 hours in the fridge.
Heat olive oil in a saucepan over a medium heat and fry onion for about 5 minutes until soft. Remove the beef from the fridge and add along with the marinade, tomatoes, potatoes and green beens. Pour over enough hot water to cover, bring to the boil, reduce the heat, cover and simmer for about 45 minutes. Stir occasionally and add water, if the stew is too dry. The stew is ready, when the vegetables are soft and the meat is tender. Remove from the heat and serve hot.